Modeling the Contribution of Gas Hydrate to Corrosion Rate Along the Subsea Pipelines

This study developed a corrosion predictive model along the deepwater gas pipelines with hydrate as the corroding agent. The model was developed and simulated with primary focus on the thermodynamic properties of each component of the gas mixture and a solution algorithm written with Matlab 6.5 (The MathWorks, Natick, MA) code. The model was validated by comparing the generated results with the outputs of already established laboratory and mathematical corrosion studies; the trends of the results obtained comparatively agreed with these studies to confirm its reliability. The model correctly predicted the relationships between corrosion rate and other thermodynamic parameters such as temperature, pressure, wall shear stress, velocity loss, and pH. This study showed that hydrates can initiate galvanic corrosion, stress cracking corrosion, and erosion-corrosion amongst others. Furthermore, the resulting corrosion rate from the hydrates could be as high as 174 mm/year (0.48 mm/day). This is extremely alarming compared to the industry’s aim to operate below 2 mm/year. At this rate, an underwater pipeline would be subjected to full bore rupture within some days if corrective measures are not quickly taken;hence, the need for further studies

Numerical simulation of the settling behaviour of particles in thixotropic fluids

A numerical study on the settling behaviour of particles in shear-thinning thixotropic fluids has been conducted. The numerical scheme was based on the volume of fluid model, with the solid particle being likened to a fluid with very high viscosity. The validity of this model was confirmed through comparisons of the flow field surrounding a sphere settling in a Newtonian fluid with the analytical results of Stokes. The rheology model for the fluid was time-dependent, utilising a scalar parameter that represents the integrity of a “structural network,” which determines its shear thinning and thixotropic characteristics. The results of this study show that the flow field surrounding the settling sphere is highly localised, with distinct regions of disturbed/undisturbed fluids. The extension of these regions depends on the relaxation time of the fluid, as well as its shear thinning characteristics, and reflects the drag force experienced by the sphere. As the sphere settles, a region of sheared fluid that has significantly lower values of viscosity is formed above the sphere. This region slowly recovers in structure in time. As a result, a sphere that falls in a partially recovered domain (e.g., due to the shearing motion of an earlier sphere) tends to attain a greater velocity than the terminal velocity value. This was found to be true even in cases where the “resting time” of the fluid was nearly twice the relaxation time of the fluid. The results of this study could provide a framework for future analysis on the time-dependent settling behaviour of particles in thixotropic shear-thinning fluids

Composite table algorithm - a powerful hybrid pinch targeting method for various problems in water integration

Water management has become a very vital issue due to stringent environmental regulations and rising cost of water resources. Pinch analysis provides a conceptual approach for water network synthesis. Targeting is the first stage in most pinch analysis techniques to provide the baseline for detailed water network design. Although Water Cascade Analysis and Material Recovery Pinch Diagram methods have been developed to handle diverse water network problems, Composite Table Algorithm (CTA) is another water pinch targeting tool with its unique combination of both numerical and graphical characteristics. CTA was originally developed for fixed flow rate problems. In this work, the applicability of CTA for various water network problems such as fixed load, mixed fixed load and fixed flow rate, multiple pinch, and threshold problem is discussed. To facilitate, the approach has been programed in MATLAB and results obtained are validated by comparing with literature

CFD simulation of solid-liquid stirred tanks for low to dense solid loading systems

The hydrodynamics of suspension of solids in liquids are critical to the design and performance of stirred tanks as mixing systems. Modelling a multiphase stirred tank at a high solids concentration is complex owing to particle-particle and particle-wall interactions which are generally neglected at low concentrations. Most models do not consider such interactions and deviate significantly from experimental data. Furthermore, drag force, turbulence and turbulent dispersion play a crucial role and need to be precisely known in predicting local hydrodynamics. Therefore, critical factors such as the modelling approach, drag, dispersion, coefficient of restitution and turbulence are examined and discussed exhaustively in this paper. The Euler-Euler approach with kinetic theory of granular flow, Syamlal-O'Brien drag model and Reynolds stress turbulence model provide realistic predictions for such systems. The contribution of the turbulent dispersion force in improving the prediction is marginal but cannot be neglected at low solids volume fractions. Inferences drawn from the study and the finalised models will be instrumental in accurately simulating the solids suspension in stirred tanks for a wide range of conditions. These models can be used in simulations to obtain precise results needed for an in-depth understanding of hydrodynamics in stirred tanks

10th international conference on gas-liquid and gas-liquid-solid reactor engineering preface

Following the success of the nine previous conferences on Gas–Liquid and Gas–Liquid–Solid reactor Engineering which were held at Columbus, OH, USA (1992), Cambridge, UK (1995), Kanagawa, Japan (1997), Delft, The Netherlands (1999), Melbourne, Australia (2001), Vancouver, Canada (2003), Strasbourg, France (2005), New Delhi, India (2007) and Montreal, Canada (2009) the tenth conference with the same theme is being held in Braga, Portugal, from 26 to 29 June 2011. This conference will cover all aspects of multiphase reactors related to progress made in the understanding, performance and operation of these reactors and will bring together scientists and engineers from universities and industry. The involvement of top researchers in Gas–Liquid and Gas–Liquid–Solid Reactor Engineering, the high quality of the papers presented and the line of continuity that has been guaranteed by the leadership of Prof. L.S. Fan of Ohio State University and the other members of the International Scientific Committee has made GLS a leading conference in Chemical Engineering. GLS has been held at regular intervals, every two years and in order to attract professionals across the globe, the venue of the GLS conference is shifted in a thoughtful manner amongst the continents. This conference has become an important meeting point for the exchange of views among scientists and engineers in one of the most important and complex issues in chemical engineering science and practice. The organizing committee is very pleased to be associated with Elsevier to have, as in most of the previous GLS editions, the proceedings of GLS10 published in Chemical Engineering Science (CES). As a result of a strict peer review process aiming at keeping with the highest standards of the journal, the GLS10 CES special issue includes a total of 39 papers, selected from the 150 Abstracts that were submitted to GLS10. Our sincere acknowledgments are due to Professor Anton P.J. Middelberg, the Executive Editor of CES, for his cooperation throughout the reviewing process. Also, we would like to express our gratitude to all the reviewers that made possible a timely publication of this special issue. Thanks are due to Genevieve Green from Elsevier for the excellent management of this special issue publication. Finally, it is our pleasure to dedicate this GLS10 CES special issue to Professor John Davidson as a tribute to his pioneering work and extraordinary contributions to Gas–Liquid and Gas–Liquid–Solid Reactor Engineering and to Chemical Engineering

Bubbles in viscous liquids: Time dependent behaviour and wake characteristics

The dynamics of a bubble, initially stationary and spherical, rising in a viscous Newtonian liquid have been studied numerically using 3-D Volume-of-Fluid (VOF) method implemented in the Gerris flow solver. The study encompasses 8.7≤Eo (=ΔρgD2/σΔρgD2/σ)≤641 and Re≤151. Additionally, results published in the literature encompassing bubbles with lower values of Eo numbers were also considered, such that the overall dependencies of bubble shape, wake characteristics, and drag coefficient over a large range of Eo and Re values can be identified. While it was found that the deformation of the bubbles as predicted through the numerical study can generally replicate experimental observations presented, several limitations were identified, such as in the representation of skirt formation behind a skirted bubble and the formation of satellite bubbles behind a bubble rising at high Reynolds numbers. The dependency of the bubble aspect ratio on the Weber and Morton numbers was confirmed for cases of spherical and ellipsoidal bubbles; whilst for spherical cap and skirted bubbles the aspect ratio was found to depend largely on the Reynolds and Capillary numbers, respectively. Finally, the expansion and formation of closed/open laminar wakes behind the rising bubble were analysed and was found to correlate well with the bubble Re and Eo numbers

Simultaneous estimation of states and inputs in a planar solid oxide fuel cell using nonlinear adaptive observer design

An adaptive nonlinear observer design for the planar solid oxide fuel cell (SOFC) is presented in this work. This observer is based on a lumped parameter model of the SOFC and it can simultaneously estimate the inputs and the states of the system. Considering the inputs as unknown parameters is advantageous because some of the input parameters are not practically measurable in a SOFC stack. The asymptotic stability of the proposed observer is proven using the Lyapunov function method and is based on the concept of input-to-state stability for cascaded systems. The simulations show that the developed observer can track the temperature and species concentration profiles in the planar SOFC during step changes in the input variables and can simultaneously predict the input variables. The adaptive observer presented is valid for a wide operating range, requires fewer variables to be measured, and is robust to fluctuations in the input variables

Hollow micro/nanomaterials as nanoreactors for photocatalysis

Learning from nature, one of the most prominent goals of photocatalysis is to assemble multifunctional photocatalytic units in an integrated, high performance device that is capable of using solar energy to produce “solar hydrogen” from aqueous media. By analogy with natural systems it is clear that scaffolds with multi-scale structural architectures are necessary. In this perspective, recent progress related to the use of hollow micro/nanomaterials as nanoreactors for photocatalysis is discussed. Organised, multi-scale assemblies of photocatalytic units on hollow scaffolds is an emerging area that shows much promise for the synthesis of high performance photocatalysts. Not only do improved transport and diffusion characteristics play an import role, but increased electron/hole separation lifetimes as well as improved light harvesting characteristics by the hollow structures also do so and are touched upon in this short perspective

The influence of corrosion inhibitors on hydrate formation temperature along the subsea natural gas pipelines

Pipeline industry annually invests millions of dollar on corrosion inhibitors in order to minimize corrosion׳s implication on flow assurance; however, attention has never been focused on the possibilities of these chemicals to promote hydrate formation along deepwater pipeline which is also a flow assurance problem. Five inhibitors were investigated in this study at different concentrations and pressures in a cryogenic sapphire cell at static condition. The changes in the formation temperature established that all the inhibitors promote hydrate but at different rates while their hydrate formation patterns also differ from one another. Their ability to promote hydrate could be attributed to their hydrogen bonding properties which is required for hydrate formation. Also, the difference in the promotion rate is attributed to their different sizes and structures, active functional groups and affinity for water molecules which determine the type of hydrogen bonding exhibited by each inhibitor while in solution. The structure and size of each inhibitor also affect its electronegativity and ionization energy since the active electrons of some of the inhibitors have direct exposure to the nucleus while for others; the active electrons at the outermost shell have been shielded from direct influence of the attractive force. Furthermore, the active functional groups obeys electronegativity trend of periodic table to determine whether the resulting bond type will be polar ionic, covalent or ionic with some covalent characteristic in nature. Though, all the inhibitors are foamy; dodecylpyridinium chloride (DPC) was however the foamiest. DPC also exhibited its highest promotion ability at 200 ppm and exhibited specific behaviour at 5000 ppm to suggest a change in the hydrate formation rate beyond the Critical Micelles Concentration (CMC). Again, increase in agitation rate prolonged the complete solidification time of the hydrates probably due to the gas solubility. Finally, the feasibility of using this chemical as an additive at high concentrations for natural gas transportation and storage in slurry form was observed due to some exhibited properties, this however requires further investigations